1. Field of the Invention
Example embodiments generally relate to a development apparatus which develops a latent image on a latent image bearer with a developer which is supported by two developer bearers, and an image forming apparatus using the development apparatus.
2. Discussion of the Background
In a conventional development apparatus, a development roller supports a developer including toner and a magnetic carrier, and the developer is conveyed by the roller to the development domain at which the development roller faces a latent image bearer. The development roller as a developer bearer has a development sleeve including a nonmagnetic pipe, which is rotated, and a magnet roller arranged inside the nonmagnetic pipe, which is not rotated with the nonmagnetic pipe. The developer is stuck to the surface of the development sleeve by the magnetism of the magnet roller. A magnetic brush is formed on the development sleeve by forming chains of a magnetic carrier in the developer using the magnetism. A tip of the magnetic brush is touched with the latent image bearer with rotation of the development sleeve, and thereby the toner on the magnetic brush is transferred to the latent image on the latent image bearer. Alternatively, the development sleeve may be fixed while rotating the magnet roller in the development sleeve.
The surface speed of latent image bearers such as photoconductors, tends to be increased more with an increase in the image formation speed in recent years. In such a high-speed image forming apparatus, if a development sleeve (or a magnet roller) is not rotated at a comparatively high speed, the amount of toner supplied to the development domain per unit time is insufficient, resulting in formation of low density images. However, if the development sleeve is rotated at comparatively high speed, wearing of the latent image bearer or the developer caused by friction between the magnetic brush and the latent image bearer becomes remarkable.
Therefore, a development apparatus using two or more development rollers, which develops a latent image on a latent image bearer, is proposed. This development apparatus includes a development chamber for developing a latent image, a first developer chamber containing the developer therein, and a second developer chamber containing the developer under the first developer chamber. The development chamber is provided beside the first developer chamber and the second developer chamber. The development chamber includes a first development roller and a second development roller under the first development roller. A first development sleeve of the first development roller supports the developer supplied from the first developer chamber beside the first development sleeve, and develops a latent image on a photoconductor serving as a latent image bearer. The developer after contributing to the development, passes through a first development domain between the first development sleeve and the photoconductor, and is transferred to the second development sleeve of the second development roller provided under the first development sleeve. Further, the developer is conveyed into the second development domain between the second development sleeve and the photoconductor with rotation of the second development sleeve, and the developer contributes to the development again. After the second contributing to the development, the developer is recovered into the second developer chamber beside the second development sleeve. The developer is then recovered into the first developer chamber.